hwlocality_memattrs(3) Hardware Locality (hwloc) hwlocality_memattrs(3)
NAME
hwlocality_memattrs - Comparing memory node attributes for finding where
to allocate on
SYNOPSIS
Data Structures
struct hwloc_location
Typedefs
typedef unsigned hwloc_memattr_id_t
Enumerations
enum hwloc_memattr_id_e { HWLOC_MEMATTR_ID_CAPACITY,
HWLOC_MEMATTR_ID_LOCALITY, HWLOC_MEMATTR_ID_BANDWIDTH,
HWLOC_MEMATTR_ID_READ_BANDWIDTH, HWLOC_MEMATTR_ID_WRITE_BANDWIDTH,
HWLOC_MEMATTR_ID_LATENCY, HWLOC_MEMATTR_ID_READ_LATENCY,
HWLOC_MEMATTR_ID_WRITE_LATENCY, HWLOC_MEMATTR_ID_MAX }
enum hwloc_location_type_e { HWLOC_LOCATION_TYPE_CPUSET,
HWLOC_LOCATION_TYPE_OBJECT }
enum hwloc_local_numanode_flag_e {
HWLOC_LOCAL_NUMANODE_FLAG_LARGER_LOCALITY,
HWLOC_LOCAL_NUMANODE_FLAG_SMALLER_LOCALITY,
HWLOC_LOCAL_NUMANODE_FLAG_ALL }
Functions
int hwloc_memattr_get_by_name (hwloc_topology_t topology, const char
*name, hwloc_memattr_id_t *id)
int hwloc_get_local_numanode_objs (hwloc_topology_t topology, struct
hwloc_location *location, unsigned *nr, hwloc_obj_t *nodes, unsigned
long flags)
int hwloc_memattr_get_value (hwloc_topology_t topology,
hwloc_memattr_id_t attribute, hwloc_obj_t target_node, struct
hwloc_location *initiator, unsigned long flags, hwloc_uint64_t
*value)
int hwloc_memattr_get_best_target (hwloc_topology_t topology,
hwloc_memattr_id_t attribute, struct hwloc_location *initiator,
unsigned long flags, hwloc_obj_t *best_target, hwloc_uint64_t *value)
int hwloc_memattr_get_best_initiator (hwloc_topology_t topology,
hwloc_memattr_id_t attribute, hwloc_obj_t target, unsigned long
flags, struct hwloc_location *best_initiator, hwloc_uint64_t *value)
Detailed Description
Platforms with heterogeneous memory require ways to decide whether a
buffer should be allocated on 'fast' memory (such as HBM), 'normal'
memory (DDR) or even 'slow' but large-capacity memory (non-volatile
memory). These memory nodes are called 'Targets' while the CPU accessing
them is called the 'Initiator'. Access performance depends on their
locality (NUMA platforms) as well as the intrinsic performance of the
targets (heterogeneous platforms).
The following attributes describe the performance of memory accesses from
an Initiator to a memory Target, for instance their latency or bandwidth.
Initiators performing these memory accesses are usually some PUs or Cores
(described as a CPU set). Hence a Core may choose where to allocate a
memory buffer by comparing the attributes of different target memory
nodes nearby.
There are also some attributes that are system-wide. Their value does not
depend on a specific initiator performing an access. The memory node
Capacity is an example of such attribute without initiator.
One way to use this API is to start with a cpuset describing the Cores
where a program is bound. The best target NUMA node for allocating memory
in this program on these Cores may be obtained by passing this cpuset as
an initiator to hwloc_memattr_get_best_target() with the relevant memory
attribute. For instance, if the code is latency limited, use the Latency
attribute.
A more flexible approach consists in getting the list of local NUMA nodes
by passing this cpuset to hwloc_get_local_numanode_objs(). Attribute
values for these nodes, if any, may then be obtained with
hwloc_memattr_get_value() and manually compared with the desired
criteria.
See also
An example is available in doc/examples/memory-attributes.c in the
source tree.
Note
The API also supports specific objects as initiator, but it is
currently not used internally by hwloc. Users may for instance use it
to provide custom performance values for host memory accesses
performed by GPUs.
The interface actually also accepts targets that are not NUMA nodes.
Typedef Documentation
typedef unsigned hwloc_memattr_id_t
A memory attribute identifier. May be either one of hwloc_memattr_id_e or
a new id returned by hwloc_memattr_register().
Enumeration Type Documentation
enum hwloc_local_numanode_flag_e
Flags for selecting target NUMA nodes.
Enumerator
HWLOC_LOCAL_NUMANODE_FLAG_LARGER_LOCALITY
Select NUMA nodes whose locality is larger than the given cpuset.
For instance, if a single PU (or its cpuset) is given in
initiator, select all nodes close to the package that contains
this PU.
HWLOC_LOCAL_NUMANODE_FLAG_SMALLER_LOCALITY
Select NUMA nodes whose locality is smaller than the given cpuset.
For instance, if a package (or its cpuset) is given in initiator,
also select nodes that are attached to only a half of that
package.
HWLOC_LOCAL_NUMANODE_FLAG_ALL
Select all NUMA nodes in the topology. The initiator initiator is
ignored.
enum hwloc_location_type_e
Type of location.
Enumerator
HWLOC_LOCATION_TYPE_CPUSET
Location is given as a cpuset, in the location cpuset union field.
HWLOC_LOCATION_TYPE_OBJECT
Location is given as an object, in the location object union
field.
enum hwloc_memattr_id_e
Memory node attributes.
Enumerator
HWLOC_MEMATTR_ID_CAPACITY
The "Capacity" is returned in bytes (local_memory attribute in
objects). Best capacity nodes are nodes with higher capacity.
No initiator is involved when looking at this attribute. The
corresponding attribute flags are HWLOC_MEMATTR_FLAG_HIGHER_FIRST.
HWLOC_MEMATTR_ID_LOCALITY
The "Locality" is returned as the number of PUs in that locality
(e.g. the weight of its cpuset). Best locality nodes are nodes
with smaller locality (nodes that are local to very few PUs). Poor
locality nodes are nodes with larger locality (nodes that are
local to the entire machine).
No initiator is involved when looking at this attribute. The
corresponding attribute flags are HWLOC_MEMATTR_FLAG_HIGHER_FIRST.
HWLOC_MEMATTR_ID_BANDWIDTH
The "Bandwidth" is returned in MiB/s, as seen from the given
initiator location. Best bandwidth nodes are nodes with higher
bandwidth.
The corresponding attribute flags are HWLOC_MEMATTR_FLAG_HIGHER_FIRST and
HWLOC_MEMATTR_FLAG_NEED_INITIATOR.
This is the average bandwidth for read and write accesses. If the
platform provides individual read and write bandwidths but no explicit
average value, hwloc computes and returns the average.
HWLOC_MEMATTR_ID_READ_BANDWIDTH
The "ReadBandwidth" is returned in MiB/s, as seen from the given
initiator location. Best bandwidth nodes are nodes with higher
bandwidth.
The corresponding attribute flags are HWLOC_MEMATTR_FLAG_HIGHER_FIRST and
HWLOC_MEMATTR_FLAG_NEED_INITIATOR.
HWLOC_MEMATTR_ID_WRITE_BANDWIDTH
The "WriteBandwidth" is returned in MiB/s, as seen from the given
initiator location. Best bandwidth nodes are nodes with higher
bandwidth.
The corresponding attribute flags are HWLOC_MEMATTR_FLAG_HIGHER_FIRST and
HWLOC_MEMATTR_FLAG_NEED_INITIATOR.
HWLOC_MEMATTR_ID_LATENCY
The "Latency" is returned as nanoseconds, as seen from the given
initiator location. Best latency nodes are nodes with smaller
latency.
The corresponding attribute flags are HWLOC_MEMATTR_FLAG_LOWER_FIRST and
HWLOC_MEMATTR_FLAG_NEED_INITIATOR.
This is the average latency for read and write accesses. If the platform
provides individual read and write latencies but no explicit average
value, hwloc computes and returns the average.
HWLOC_MEMATTR_ID_READ_LATENCY
The "ReadLatency" is returned as nanoseconds, as seen from the
given initiator location. Best latency nodes are nodes with
smaller latency.
The corresponding attribute flags are HWLOC_MEMATTR_FLAG_LOWER_FIRST and
HWLOC_MEMATTR_FLAG_NEED_INITIATOR.
HWLOC_MEMATTR_ID_WRITE_LATENCY
The "WriteLatency" is returned as nanoseconds, as seen from the
given initiator location. Best latency nodes are nodes with
smaller latency.
The corresponding attribute flags are HWLOC_MEMATTR_FLAG_LOWER_FIRST and
HWLOC_MEMATTR_FLAG_NEED_INITIATOR.
Function Documentation
int hwloc_get_local_numanode_objs (hwloc_topology_t topology, struct
hwloc_location * location, unsigned * nr, hwloc_obj_t * nodes, unsigned
long flags)
Return an array of local NUMA nodes. By default only select the NUMA
nodes whose locality is exactly the given location. More nodes may be
selected if additional flags are given as a OR'ed set of
hwloc_local_numanode_flag_e.
If location is given as an explicit object, its CPU set is used to find
NUMA nodes with the corresponding locality. If the object does not have a
CPU set (e.g. I/O object), the CPU parent (where the I/O object is
attached) is used.
On input, nr points to the number of nodes that may be stored in the
nodes array. On output, nr will be changed to the number of stored nodes,
or the number of nodes that would have been stored if there were enough
room.
Note
Some of these NUMA nodes may not have any memory attribute values and
hence not be reported as actual targets in other functions.
The number of NUMA nodes in the topology (obtained by
hwloc_bitmap_weight() on the root object nodeset) may be used to
allocate the nodes array.
When an object CPU set is given as locality, for instance a Package,
and when flags contain both HWLOC_LOCAL_NUMANODE_FLAG_LARGER_LOCALITY
and HWLOC_LOCAL_NUMANODE_FLAG_SMALLER_LOCALITY, the returned array
corresponds to the nodeset of that object.
int hwloc_memattr_get_best_initiator (hwloc_topology_t topology,
hwloc_memattr_id_t attribute, hwloc_obj_t target, unsigned long flags,
struct hwloc_location * best_initiator, hwloc_uint64_t * value)
Return the best initiator for the given attribute and target NUMA node.
If the attribute does not relate to a specific initiator (it does not
have the flag HWLOC_MEMATTR_FLAG_NEED_INITIATOR), -1 is returned and
errno is set to EINVAL.
If value is non NULL, the corresponding value is returned there.
If multiple initiators have the same attribute values, only one is
returned (and there is no way to clarify how that one is chosen).
Applications that want to detect initiators with identical/similar
values, or that want to look at values for multiple attributes, should
rather get all values using hwloc_memattr_get_value() and manually select
the initiator they consider the best.
The returned initiator should not be modified or freed, it belongs to the
topology.
flags must be 0 for now.
If there are no matching initiators, -1 is returned with errno set to
ENOENT;
int hwloc_memattr_get_best_target (hwloc_topology_t topology,
hwloc_memattr_id_t attribute, struct hwloc_location * initiator, unsigned
long flags, hwloc_obj_t * best_target, hwloc_uint64_t * value)
Return the best target NUMA node for the given attribute and initiator.
If the attribute does not relate to a specific initiator (it does not
have the flag HWLOC_MEMATTR_FLAG_NEED_INITIATOR), location initiator is
ignored and may be NULL.
If value is non NULL, the corresponding value is returned there.
If multiple targets have the same attribute values, only one is returned
(and there is no way to clarify how that one is chosen). Applications
that want to detect targets with identical/similar values, or that want
to look at values for multiple attributes, should rather get all values
using hwloc_memattr_get_value() and manually select the target they
consider the best.
flags must be 0 for now.
If there are no matching targets, -1 is returned with errno set to
ENOENT;
Note
The initiator initiator should be of type HWLOC_LOCATION_TYPE_CPUSET
when refering to accesses performed by CPU cores.
HWLOC_LOCATION_TYPE_OBJECT is currently unused internally by hwloc,
but users may for instance use it to provide custom information about
host memory accesses performed by GPUs.
int hwloc_memattr_get_by_name (hwloc_topology_t topology, const char * name,
hwloc_memattr_id_t * id)
Return the identifier of the memory attribute with the given name.
int hwloc_memattr_get_value (hwloc_topology_t topology, hwloc_memattr_id_t
attribute, hwloc_obj_t target_node, struct hwloc_location * initiator,
unsigned long flags, hwloc_uint64_t * value)
Return an attribute value for a specific target NUMA node. If the
attribute does not relate to a specific initiator (it does not have the
flag HWLOC_MEMATTR_FLAG_NEED_INITIATOR), location initiator is ignored
and may be NULL.
flags must be 0 for now.
Note
The initiator initiator should be of type HWLOC_LOCATION_TYPE_CPUSET
when refering to accesses performed by CPU cores.
HWLOC_LOCATION_TYPE_OBJECT is currently unused internally by hwloc,
but users may for instance use it to provide custom information about
host memory accesses performed by GPUs.
Author
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source code.
Version 2.9.1 Tue Mar 28 2023 hwlocality_memattrs(3)
hwloc 2.9.1 - Generated Fri Apr 21 05:51:45 CDT 2023